This is from another site. Just an FYI
"The greenish hue is actually chlorophyll, but it is also an indicator that an alkaloid, called solanine, may be present under the skin of the potato. Solanine develops in potatoes when they are stored in the presence of light (which also encourages chlorophyll formation) and either at very cold or quite warm temperatures. It is toxic, however it would take a very large number of green potatoes to make you ill. This apllies to the green sprouts and skin.
Since solanine collects just under the skin, it is safe to peel away the skin and a thin layer of white flesh before you cook the potato. Cooking at high temperatures (over 170 °C or 340 °F) partly destroys these.Believe it or not, potatoes are part of the deadly nightshade family. While it can make someone ill, its also poisonious to dogs . "